Earthquake Rupture at Focal Depth, Part I: Structure and Rupture of the Pretorius Fault, Tautona Mine, South Africa
Pure Appl. Geophys. 168 (2011), 2395–2425 Ó 2011 Springer Basel AG DOI 10.1007/s00024-011-0354-7 Pure and Applied Geophysics Earthquake Rupture at Focal Depth, Part I: Structure and Rupture of the Pretorius Fault, TauTona Mine, South Africa 1,2 1,3 1 V. HEESAKKERS, S. MURPHY, and Z. RECHES Abstract—We analyze the structure of the Archaean Pretorius 1. Introduction fault in TauTona mine, South Africa, as well as the rupture-zone that recently reactivated it. The analysis is part of the Natural Earthquake Laboratory in South African Mines (NELSAM) project Fault-zones typically move by infrequent earth- that utilizes the access to 3.6 km depth provided by the mining quakes that are localized along weak surfaces and operations. The Pretorius fault is a *10 km long, oblique-strike- separated by inter-seismic periods of tens to thou- slip fault with displacement of up to 200 m that crosscuts fine to very coarse grain quartzitic rocks in TauTona mine. We identify sands of years. Fault healing between earthquakes here three structural zones within the fault-zone: (1) an outer may renew fault strength and its rupture resistance damage zone, *100 m wide, of brittle deformation manifested by (MARONE, 1998;MUHURI et al., 2003;SIBSON, 1985). multiple, widely spaced fractures and faults with slip up to 3 m; (2) an inner damage zone, 25–30 m wide, with high density of anas- This earthquake cycle terminates when the fault tomosing conjugate sets of fault segments and fractures, many of becomes quiescent due primarily to changes in tectonic which carry cataclasite zones; and (3) a dominant segment, with a activity.
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